Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y11: Swimming, Motility and Locomotion IIRecordings Available
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Sponsoring Units: DFD Chair: Tom Solomon, Bucknell University Room: McCormick Place W-181B |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y11.00001: Q-tensor model for undulatory swimming in lyotropic liquid-crystalline polymers Tong Gao Microorganisms may exhibit rich swimming behaviors in anisotropic fluids, such as liquid crystals, that have direction-dependent physical and rheological properties. Here we construct a two-dimensional computation model to study the undulatory swimming mechanisms of microswimmers in a solution of rigid, rodlike liquid-crystalline polymers. We describe the fluid phase using Doi's Q-tensor model, and treat the swimmer as a finite-length flexible fiber with imposed propagating traveling waves on the body curvature. The fluid-structure interactions are resolved via an Immersed Boundary method. Compared to the swimming dynamics in Newtonian fluids, we observe non-Newtonian behaviors that feature both enhanced and retarded swimming motions in lyotropic liquid-crystalline polymers. We reveal the propulsion mechanism by analyzing the near-body flow fields and polymeric force distributions, together with asymptotic analysis for an idealized model of Taylor's swimming sheet. |
Friday, March 18, 2022 8:12AM - 8:24AM |
Y11.00002: Magnetic filaments: shapes, stability and self-propulsion Andrejs Cebers, Abdelqader Zaben, Guntars Kitenbergs, Mihails Belovs Flexible magnetic rods are studied from different points of view. For the rod with remanent magnetization and paramagnetic susceptibility the equilibrium configurations with free and unclamped ends are calculated. It is shown by the analysis of the corresponding eigenvalue problems that these shapes are unstable. In order to avoid this instability when the ferromagnetic swimmer is realized experimentally and exhibits the self-propelling motion that occurs due to the U-like deformation and its relaxation, the duration of the pulse of the driving magnetic field during which the deformation develops is shortened relative to the part of the cycle that corresponds to the relaxation of the U-like shape. The experimentally observed dynamics of the shapes is in good agreement with numerical simulations if the ratio of the perpendicular and parallel drag coefficients is taken as 1.3 instead of 2. The mechanism of propulsion of the ferromagnetic rod is similar to that of Chlamydomonas and is based on the non-reciprocity of the bending and relaxation stages as found both experimentally and numerically. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y11.00003: Extracting hydrodynamic properties of microscale helical filament from Brownian motion using light-sheet microscopy Rizal F Hariadi A motile microscopic object, such as a swimming bacteria, experiences both Stokes flow and thermal fluctuations. While both physical processes occur simultaneously, they are often studied separately. Using the fluctuation-dissipation theorem, here we show how an analytical method combined with experimental results can determine the propulsion matrix of a single rigid microscale filament, namely E. Coli flagellum, using the Brownian motion analysis. A high resolution, single-objective light-sheet microscopy technique capable of recording a 3D movie at up to 26 volumes/sec, was used to measure the translational and rotational diffusion of an isolated individual fluorescent flagellum extracted from E. coli. Our measurements show that the propulsion matrix elements derived from analyzing the flagellum are two orders of magnitude smaller than those obtained by measurement of trapped living E. coli by optical tweezers. In addition, our preliminary data for 3D diffusion measurement revealed translational diffusion close to the surface is modified by hydrodynamic interactions between the helical filament and the boundary. At a distance of 15±3 μm from the surface, the flagellum with an average length of 7 μm diffuse at a similar rate (p-value=0.37, N=7) on its major axis (D‖=0.21±0.04 μm2/sec) and the two orthogonal axes (D⊥=0.20±0.03 μm2/sec). Doubling the distance to 30±3 μm from the surface leads to flagella diffusing nearly twice as fast (p-value=0.004, N=10) along its major axis (D‖=0.30±0.05 μm2/sec) compared to the two orthogonal axes (D⊥=0.16±0.02 μm2/sec). Our work shows that beyond measuring diffusion constants, thermal fluctuation can provide information about the propulsion matrix of microscale objects. Broadly, our findings show that the hydrodynamic evaluation of organisms at low Reynolds numbers in crowded environments can be determined from their Brownian motion without enforcing any fluid flow, which is impractical in a complex biological milieu. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y11.00004: The role of surface properties and internal degrees of freedom on the thermophoresis of Janus particles Juan D Olarte-Plata, Fernando Bresme From the early observations of thermodiffusion by Ludwig and Soret [1,2] to the study of thermal polarization [3,4], temperature fields have been identified as key molecular driving forces. In this context, Janus particles have received much attention due to their tunable heterogeneity, which determines their thermal response and motion rectification. While theoretical work on Janus particles has focused on surface properties [5], we have shown that the internal mass distribution plays an important role in the thermal orientation effect [6]. In this work, we demonstrate how both interfacial properties as well as internal degrees of freedom must be considered in order to understand the emerging behaviour of Janus colloids under temperature gradients, opening new avenues for their rational design. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y11.00005: Investigating the Force-transduction Mechanism Driving Gravi-kinesis in a Swimming Ciliated Protist Jim M Valles, Nicholas Conroy, Christopher Turner, Adrian Rogel Ciliated protists often exhibit negative gravi-kinesis. Paramecium caudatum, for example, propel themselves more strongly when swimming against gravity and less when swimming with gravity. While the difference between up and down propulsions scales linearly with the apparent weight (w), it is not clearly established how paramecia sense this very small force (w ~ 100 pN in water). According to the prevailing mechanism, the full body statocyst model (FBS), the cytoplasm acts like a statocyst that distorts the cell membrane with the force w. The distortions, depend on orientation altering ion channel conduction to change the cell membrane potential, which controls ciliary beating. Concerns about whether the w-induced stresses are sufficiently large to overcome thermal noise have led us to consider an alternative model. In the alternative Sedimentation Stress Sensing Model (SSS), sedimentation-induced shear stresses (which are also orientation-dependent and proportional to w) cause the changes in motile cilia beating.* We will describe how studies of gravi-kinesis in confining geometries are promising for discerning between the FBS and SSS models, as well as available results. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y11.00006: Calibrating the method of images for regularized Stokeslets using dynamically similar experiments Bruce E Rodenborn, Nicholas G Coltharp, Hoa Nguyen, Frank Healy, Orrin Shindell Many bacteria use a helical flagellum for propulsion and when bacteria approach a boundary, the forces and torques exerted by the fluid increase rapidly. The method of images for regularized Stokeslets (MIRS) is often used to model such bacterial swimming near a boundary. The method includes both discretization and regularization parameters, but there is no theory that predicts the appropriate regularization parameter for a given surface discretization of a solid object. The choice has generally been made without precise connection to real-world experiments. Thus, we used dynamically similar macroscopic experiments to calibrate MIRS for our model of a bacterium, which has a cylindrical body and a helical flagellum. We have measured the torque on constrained rotating cylinders and constrained rotating helices at various distances from a solid boundary. We have thereby verified, for the first time, the theory of Jeffrey and Onishi (1981) for the torque on a rotating cylinder near a plane wall. We then used theory and the experiments to determine optimal discretization and regularization parameters for MIRS for these two geometries. The average mean-square error between our experiments and simulations is less than 5%. Our technique allows us to extract accurate predictions of forces and torques from our model of a swimming bacterium to assess various efficiency measures as a function of boundary distance and body/flagellum geometry, as presented in Shindell et al., Fluids (2021), and discussed in the same session by Orrin Shindell. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y11.00007: Order in fish collective motion is modified by environnement illuminance Benjamin Thiria, Baptiste LAFOUX, Ramiro Godoy-Diana The level of order in animal groups on the move can display a wide range of variations, from fully disorganized aggregates to regular networks. This collective motion could not be achieved if individuals were assessing their environment independently; instead, it emerges due to interactions within the group. Ability to organize thus strongly depends on disturbance of the environment, which can alter how group members perceive their neighbors. For fish schools, information collection relies on sensory mechanisms, namely vision and flow sensing. However, quantitative description of sensory thresholds leading to schooling state transition is still lacking. We show that the group structure of rummy-nose tetra (Hemigrammus rhodostomus) exhibits distinct dynamics depending on the illumination of their habitat. Free swimming assemblies of ca. 50 fish are recorded in a large tank, where illuminance level is adjusted from 0 to 900 lux. We quantify geometrical order with polarization and milling parameters, which capture global alignment and rotation: for low light exposure, we observe little to no order; intensity of the collective motion then increases with illumination, until a threshold. Our data suggest that vision capability plays a major role in the level of order of a fish school. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y11.00008: Macroscopic robophysical model of biflagellate algae's phototactic turning Tommie L Robins, Kelimar Diaz, Kirsty Y Wan, Daniel I Goldman Algae exhibit diverse behaviors in their locomotion. For phototaxis, green-celled algae possess a light-triggered response that allows the turning of their eyespot towards a light source. The photoreceptor responsible for this type of behavior is well documented, however, the mechanical flagellar response is not. In Chlamydomonas, studies suggest that during a phototactic response, there is a change in beating frequency of the cis (the flagella closest to the eyespot) and trans flagella (Witman, 1996). To study phototactic turning, we developed a macroscopic motor-driven robophysical model that swims in a viscous fluid (glycerin, 1,100 cSt) to replicate low Reynolds number swimming. We achieve rotation by varying the frequency of the trans flagellum while maintaining a constant frequency of the cis. We observed that the efficacy of phototaxis depends on the phase position of the cis flagella. While the cis flagellum was in its recovery phase, the robot rotated 23-34 degrees per cycle (deg/cyc). While in the power phase, the robot rotated 8-13 deg/cyc. The results suggest turning dependence on flagellar coordination. Preliminary experiments suggest feedback control can be implemented in the robot to generate autonomous phototactic turning. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y11.00009: TMD-Material-Integrated Micromachines: Synthesis, Propulsion, and Application Donglei Emma Fan The pursuit of artificial micro/nanoscale intelligent machines that can carry out multi-tasks demands the fabrication and integration of innovative functional materials. In the past decades, transition metal dichalcogenide (TMD) materials, such as molybdenum disulfide (MoS2), have received immense attention owing to their unique electrical, catalytic, biological, and mechanical properties for myriad applications. Nevertheless, TMD materials have been rarely explored in the research of micro/nanomachines, the success of which could bring unparallel opportunities to basic research and applications in micro/nanorobotics. Herein, we report the design, fabrication, and performance of an original one-side-open MoS2/TiO2 hollow Janus micromotor (OHJM) that autonomously propels in an aqueous solution with light simulation. Owing to the unique type-II bandgap alignment of the MoS2/TiO2 heterojunction, the OHJMs exhibit enhanced propulsion due to an extended light absorption to the visible region. They also demonstrate anomalous speed acceleration in response to an ionic environment, observed for the first time among various chemical-driven micromotors. Finally, the MoS2/TiO2 micromotors are applied for water treatment and disinfect 99.999% of E. coli in one hour. This research highlights the potentials of TMD materials for both the fundamental investigation and applications of micro/nanomachines. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y11.00010: Patchy Microrobots for Precise Micromanipulation David P Rivas Micrororobots show promise as useful tools in applications ranging from drug delivery to micromanipulation to environmental remediation. Having the advantage of being relatively powerful, fast, and readily fabricated, spherical bubble-propelled microrobots, which are driven by the catalytic decomposition of a fuel source in their environment, are particularly well suited for many of these applications. One hurdle in using these microrobots in applications requiring precise manipulation at the microscale is the quasi-oscillatory motion of the microrobot produced by the cyclical bubble growth and burst process, as well as the interference created by the presence of the bubbles themselves. Using a simple glancing-angle deposition technique, we have fabricated novel patchy microrobots that display smoother trajectories with smaller bubble size, making them suitable for precise micromanipulation. We demonstrate the use of these microrobots by manipulating and assembling passive objects at the air-liquid interface as well as on a substrate. We also study the particle and bubble dynamics which lends insight into the process of bubble creation and dissolution, which could be useful in designing other microrobots in the future. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y11.00011: Acoustically powered bubble microactuator for robotic manipulation Amit Dolev, Murat Kaynak, Selman Sakar Oscillating microbubbles generate mean flow, which is known as acoustic streaming (AS), that results in counteracting thrust applied to the bubble. Unlike spherical bubbles, entrapped bubbles with several gas-fluid interfaces can generate directed AS, hence, spatiotemporally controlled thrust. Formulating a fluid-structure interaction model capturing multiple continuous interfaces enables the prediction of the bubble’s natural frequencies (NFs). This calculation is critical because exciting the bubble at the NFs optimizes the performance. We developed a microscopic actuator comprising an entrapped bubble with three interfaces. Its geometry was carefully designed such that at each NF one opening is predominantly deformed, resembling the first vibration mode of a membrane. We used numerical simulations to estimate the generated thrust (i.e., magnitude and direction) due to an impinging planar pressure wave as a function of the excitation frequency. To validate the methodology, a microactuator is 3D printed atop an ultraflexible microcantilever beam using two-photon lithography. Leveraging the principle of superposition, we applied an acoustic field in the form of a combination of three harmonic terms to have the actuator follow complex trajectories with high accuracy. |
Friday, March 18, 2022 10:12AM - 10:24AM |
Y11.00012: Artificial microswimmers via reinforcement learning Zonghao Zou, Yuexin Liu, On Shun Pak, Yuan-Nan Young, Alan Cheng Hou Tsang There is a growing interest in developing artificial microswimmers that can self-propel like swimming microorganisms for potential biomedical applications. A fundamental challenge is the design of effective locomotory gaits that can overcome the constraints due to the dominance of viscous forces. In addition, the swimmer needs to adapt its gaits in order to re-orient and reach the target locations. In this talk, we report our progress in integrating machine learning techniques in the design of artificial microswimmers. We will discuss how reinforcement learning can be leveraged to enable complex maneuvers of the swimmer. The results demonstrate the vast potential of this new approach in designing smart microswimmers that can perform sophisticated tasks. |
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